We have found in preliminary experiments, that modest modifications of a chick's visual experience can cause severe axial myopia. Specifically restricting vision to the frontal visual field causes up to 24 diopters of myopia and a mean increase of 14% in the axial length of the eye, whereas restricting vision to the lateral field has no effect. We know of no other instance of specific visual experience producing extreme myopia. We propose, first, to characterize more fully the morphological change in the eye (axial length, spacing of the refractive elements, curvature of lens and cornea) as this myopic conditions develops, in order to discover what changes occur first and to assess the relationship of this condition to the avian glaucoma syndrome. Next, we plan to determine what aspect of the altered visual experience is responsible for the effect. Light intensity, retinal location ocular accomodation and convergence will be manipulated. We also plan to investigate the developmental course of the effect at what point in development are the animals most affected and how short a period of altered visual experience can produce myopia. Finally we hope to study the physiological processes mediating the effect of the visual experience on the anatomical changes.